1. Field of the Invention
This invention relates generally to storage and dispensing systems for the selective dispensing of fluids from a vessel or storage container in which the fluid component(s) are held in sorptive relationship to a solid carbon sorbent medium having low adsorption Heels, and are desorptively released from the carbon sorbent medium in the dispensing operation.
2. Description of the Related Art
In a wide variety of industrial processes and applications, there is a need for a reliable source of process fluid(s).
Such process and application areas include semiconductor manufacturing, ion implantation, manufacture of flat panel displays, medical intervention and therapy, water treatment, emergency breathing equipment, welding operations, space-based delivery of liquids and gases, etc.
U.S. Pat. No. 4,744,221 issued May 17, 1988 to Karl O. Knollmueller discloses a method of storing and subsequently delivering arsine, by contacting arsine at a temperature of from about xe2x88x9230xc2x0 C. to about +30xc2x0 C. with a zeolite of pore size in the range of from about 5 to about 15 Angstroms to adsorb arsine on the zeolite, and then dispensing the arsine by heating the zeolite to an elevated temperature of up to about 175xc2x0 C. for sufficient time to release the arsine from the zeolite material.
The method disclosed in the Knoilmueller patent is disadvantageous in that it requires the provision of heating means for the zeolite material, which must be constructed and arranged to heat the zeolite to sufficient temperature to desorb the previously sorbed arsine from the zeolite in the desired quantity.
The use of a heating jacket or other means exterior to the vessel holding the arsine-bearing zeolite is problematic in that the vessel typically has a significant heat capacity, and therefore introduces a significant lag time to the dispensing operation. Further, heating of arsine causes it to decompose, resulting in the formation of hydrogen gas, which introduces an explosive hazard into the process system. Additionally, such thermally-mediated decomposition of arsine effects substantial increase in gas pressure in the process system, which may be extremely disadvantageous from the standpoint of system life and operating efficiency, as well as safety concerns.
The provision of interiorly disposed heating coil or other heating elements in the zeolite bed itself is problematic since it is difficult with such means to uniformly heat the zeolite bed to achieve the desired uniformity of arsine gas release.
The use of heated carrier gas streams passed through the bed of zeolite in its containment vessel may overcome the foregoing deficiencies, but the temperatures necessary to achieve the heated carrier gas desorption of arsine may be undesirably high or otherwise unsuitable for the end use of the arsine gas, so that cooling or other treatment is required to condition the dispensed gas for ultimate use.
U.S. Pat. No. 5,518,528 issued May 21, 1996 in the names of Glenn M. Tom and James V. McManus, describes a gas storage and dispensing system, for the storage and dispensing of gases, which overcomes the above-discussed disadvantages of the gas supply process disclosed in the Knollmueller patent. The gas storage and dispensing system of the Tom et al. patent comprises an adsorption-desorption apparatus, for storage and dispensing of a gas, e.g., a gas selected from the group consisting of hydride gases, halide gases, and organometallic Group V compounds, including: a storage and dispensing vessel constructed and arranged for holding a solid-phase physical sorbent medium, and for selectively flowing gas into and out of said vessel; a solid-phase physical sorbent medium disposed in said storage and dispensing vessel at an interior gas pressure; a sorbate gas physically adsorbed on the solid-phase physical sorbent medium; a dispensing assembly coupled in gas flow communication with the storage and dispensing vessel, and constructed and arranged to provide, exteriorly of the storage and dispensing vessel, a pressure below said interior pressure, to effect desorption of sorbate gas from the solid-phase physical sorbent medium, and gas flow of desorbed gas through the dispensing assembly.
The storage and dispensing vessel of the Tom et al. patent embodies a substantial advance in the art, relative to the prior art use of high pressure gas cylinders. Conventional high pressure gas cylinders are susceptible to leakage from damaged or malfunctioning regulator assemblies, as well as to rupture if internal decomposition of the gas leads to rapid increasing interior gas pressure in the cylinder and the risk of cylinder rupture or other unwanted bulk release of gas from the cylinder. The gas storage and dispensing vessel of the Tom et al. patent reduces the pressure of stored sorbate gases by reversibly adsorbing them onto a carrier sorbent medium such as a zeolite or activated carbon material.
The efficiency of the fluid storage and delivery system of the Tom et al. patent is directly affected by the sorbent material employed therein. Therefore, there is a continuing need in the art to identify and utilize improved sorbent materials in such fluid storage and delivery systems, and it is accordingly an object of the present invention to provide a fluid storage and dispensing system utilizing a high efficiency sorbent material which offers significant advantages in cost, ease of use, and performance characteristics.
The present invention contemplates a system for storage and dispensing of a sorbable fluid, e.g., a gas, vapor, liquid, multiphase fluid, etc., including fluid mixtures as well as single component fluids.
In one aspect, the invention relates to an adsorption-desorption apparatus, which comprises a storage and dispensing vessel for holding a low Heel carbon sorbent medium therein at an interior gas pressure, a sorbable fluid physically adsorbed on said low Heel carbon sorbent medium; and a dispensing assembly coupled in gas flow communication with the storage and dispensing vessel and arranged for dispensing from the vessel sorbable fluid desorbed from the solid-phase carbon sorbent medium.
The term xe2x80x9cHeelxe2x80x9d is defined herein as the amount of residual sorbate fluid (in grams) that is retained by a sorbent material after desorption, under a certain pressure and at a certain temperature, per unit volume (in liters) of bed of the sorbent material, which is considered irremovable or disproportionately difficult to remove from the sorbent material. This portion of sorbate fluid constitutes waste and reduces the sufficiency of the fluid storage and dispensing system.
The phrase xe2x80x9clow Heelxe2x80x9d as used in the present application is defined as being characterized by at least one of the following: (i) Heel, measured for gaseous arsine (AsH3) at 20xc2x0 C. at 20 Torr, of not more than 50 grams AsH3 per liter of bed of the sorbent material; (ii) Heel, measured for gaseous boron trifluoride (BF3) at 20xc2x0 C. at 20 Torr, of not more than 20 grams boron trifloride per liter of bed of the sorbent material; (iii) Heel, measured for gaseous germanium tetrafluoride (GeF4) at 20xc2x0 C. at 20 Torr, of not more than 250 grams GeF4 per liter of bed of the sorbent material; (iv) Heel, measured for gaseous arsenic pentafluoride (AsF5) at 20xc2x0 C. at 20 Torr, of not more than 700 grams AsF5 per liter of bed of the sorbent material; (v) Heel, measured for gaseous trimethyl silane (3MS) at 20xc2x0 C. at 20 Torr, of not more than 160 grams 3MS per liter of bed of the sorbent material; and (vi) Heel, measured for gaseous ethane (C2H6) at 21xc2x0 C. at 25 Torr, of not more than 10 grams ethane per liter of bed of the sorbent material.
Preferably, the carbon sorbent material employed by the present invention has both a low Heel and a high Sorbent Working Capacity.
The phrase xe2x80x9cSorbent Working Capacityxe2x80x9d (Cw) is defined herein as the amount of sorbate fluid (in grams) originally loaded on the sorbent medium that is removable from the sorbent medium in the fluid dispensing operation, when the pressure is reduced from a higher pressure to a lower pressure at a certain temperature. For example, the Sorbent Working Capacity per unit volume (in liters) of the sorbent material, when the pressure decreases from 650 Torr to 20 Torr at 20xc2x0 C., is illustrated by the following equation:       C    W    =      xe2x80x83    ⁢                                                                        Amount                ⁢                                  xe2x80x83                                ⁢                of                ⁢                                  xe2x80x83                                ⁢                Sorbate                ⁢                                  xe2x80x83                                ⁢                Originally                ⁢                                  xe2x80x83                                ⁢                Loaded                                                                                                          (                                      at                    ⁢                                          xe2x80x83                                        ⁢                    650                    ⁢                                          xe2x80x83                                        ⁢                    Torr                                    )                                -                                  Heel                  ⁢                                      xe2x80x83                                    ⁢                                      (                                          at                      ⁢                                              xe2x80x83                                            ⁢                      20                      ⁢                                              xe2x80x83                                            ⁢                      Torr                                        )                                                                                      ⁢                  xe2x80x83                            Volume        ⁢                  xe2x80x83                ⁢        of        ⁢                  xe2x80x83                ⁢        Sorbent        ⁢                  xe2x80x83                ⁢        Material              ⁢          xe2x80x83        ⁢          (              at        ⁢                  xe2x80x83                ⁢                  20          ∘                ⁢                  xe2x80x83                ⁢                  C          .                    )      
As used in such determination, the sorbent material volume is the volume of a bed of the sorbent material.
The phrase xe2x80x9chigh Sorbent Working Capacityxe2x80x9d as used in the present application is defined as being characterized by at least one of the following: (i) Sorbent Working Capacity, measured for gaseous arsine (AsH3) at 20xc2x0 C from 650 Torr to 20 Torr, of at least 260 grams AsH3 per liter of bed of the sorbent material; (ii) Sorbent Working Capacity, measured for gaseous boron trifluoride (BF3) at 20xc2x0 C. from 650 Torr to 20 Torr, of at least 50 grams of BF3 per liter of bed of the sorbent material; (iii) Sorbent Working Capacity, measured for gaseous germanium tetrafluoride (GeF4) at 20xc2x0 C. from 650 Torr to 20 Torr, of at least 350 grams GeF4 per liter of bed of the sorbent material; (iv) Sorbent Working Capacity, measured for gaseous arsenic pentafluoride (AsF5) at 20xc2x0 C. from 650 Torr to 20 Torr, of at least 150 grams AsF5 per liter of bed of the sorbent material; and (v) Sorbent Working Capacity, measured for gaseous trimethyl silane (3MS) at 20xc2x0 C. from 650 Torr to 20 Torr, of at least 70 grams 3MS per liter of bed of the sorbent material.
Another aspect of the present invention relates to an adsorption-desorption apparatus as described hereinabove, which comprises a carbon sorbent medium having low sorption waste rate.
The term xe2x80x9csorption waste ratexe2x80x9d is defined herein as the percentage of a sorbate fluid that is irremovably retained by the sorbent medium after desorption (i.e. Heel), over the total amount of such sorbate fluid that is originally loaded on the sorbent medium before desorption, when the pressure decreases from a higher pressure to a lower pressure at a certain temperature. The sorption waste rate (Rw), when measured from 650 Torr to 20 Torr at 20xc2x0 C., is illustrated by the following equation:       R    W    =      xe2x80x83    ⁢                    Heel        ⁢                  xe2x80x83                ⁢                  (                      at            ⁢                          xe2x80x83                        ⁢            20            ⁢                          xe2x80x83                        ⁢            Torr                    )                                                                                Sorbate                ⁢                                  xe2x80x83                                ⁢                Working                ⁢                                  xe2x80x83                                ⁢                Capacity                            ⁢                              xe2x80x83                                                                                                        (                                  from                  ⁢                                      xe2x80x83                                    ⁢                  650                  ⁢                                      xe2x80x83                                    ⁢                  Torr                  ⁢                                      xe2x80x83                                    ⁢                  to                  ⁢                                      xe2x80x83                                    ⁢                  20                  ⁢                                      xe2x80x83                                    ⁢                  Torr                                )                            +                              Heel                ⁢                                  xe2x80x83                                ⁢                                  (                                      at                    ⁢                                          xe2x80x83                                        ⁢                    20                    ⁢                                          xe2x80x83                                        ⁢                    Torr                                    )                                                                          ⁢          xe2x80x83        ⁢    %    ⁢          xe2x80x83        ⁢          (              at        ⁢                  xe2x80x83                ⁢                  20          ∘                ⁢                  xe2x80x83                ⁢                  C          .                    )      
The phrase xe2x80x9clow sorption waste ratexe2x80x9d as used in the present application is defined as being characterized by at least one of the following: (i) sorption waste rate, measured for arsine (AsH3) at 20xc2x0 C. from 650 Torr to 20 Torr, of not more than 20% (preferably of not more than 15%, and more preferably of not more than 12%); (ii) sorption waste rate, measured for boron trifluoride (BF3) at 20xc2x0 C. from 650 Torr to 20 Torr, of not more than 38%; (iii) sorption waste rate, measured for germanium tetrafluoride (GeF4) at 20xc2x0 C. from 650 Torr to 20 Torr, of not more than 40% (preferably of not more than 35%, and more preferably of not more than 30%); (iv) sorption waste rate, measured for arsenic pentafluoride (AsF5) at 20xc2x0 C. from 650 Torr to 20 Torr, of not more than 75% (preferably of not more than 70%); and (v) sorption waste rate, measured for trimethyl silane (3MS) at 20xc2x0 C. from 650 Torr to 20 Torr, of not more than 60% (preferably of not more than 55%, and more preferably of not more than 45%).
The carbon sorbent material useful in the adsorption-desorption apparatus of the present invention can have any suitable size, shape, and conformation, including bead, granules, pellets, tablets, powders, particulates, extrudates, cloth or web form materials, honeycomb matrix monolith, composites of the carbon sorbent with other components, as well as comminuted or crushed forms of the foregoing conformations. Preferably such carbon sorbent materials comprise bead carbon particles of a highly uniform spherical shape.
The apparent density of the carbon sorbent material employed by the present invention is preferably less than 0.5 g/cc. The ash content is preferably below about 6% by weight, based on the total weight of the carbon sorbent material, prefereably below 1%, more preferably below about 0.1%, and most preferably about 0%.
Moisture contained by the carbon sorbent material may decompose the sorbate fluid in the storage and dispensing system of the present invention and therefore causes undesirable waste of the sorbate as well as lead to pressure rise within the storage and dispensing vessel. Therefore, the carbon sorbent material employed by the present invention desirably has moisture content of not more than 0.04% by weight, and more preferably 0%.
The dispensing assembly of the adsorption-desorption apparatus of the present invention is coupled with the storage and dispensing vessel in gas flow communication and arranged for dispensing from said vessel sorbable fluid desorbed from the solid-phase low Heel carbon sorbent medium. Such dispensing assembly may be constructed and arranged to provide, exteriorly of the storage and dispensing vessel, a pressure below the interior pressure, to effect pressure differential desorption of fluid from the solid-phase low Heel carbon sorbent medium, and fluid flow of desorbed fluid through the dispensing assembly.
Alternatively, the dispensing assembly may comprise means for selectively heating the low Heel carbon sorbent material, to effect thermal desorption of the fluid from such carbon sorbent medium, and flow of the thermally desorbed fluid through the dispensing assembly.
As a further alternative, the dispensing assembly may be constructed and arranged to effect a combination of thermal and pressure differential desorption of the fluid from the solid-phase low Heel carbon sorbent medium.
In yet another alternative arrangement, the dispensing assembly may be arranged to flow a carrier fluid therethrough, so that the resultant mass transfer gradient effects desorption of the sorbate fluid from the carbon sorbent medium, to thereby dispense the sorbate fluid as a component of the carrier fluid stream discharged from the vessel.
The dispensing assembly of the present invention may comprise any appropriate means, including without limitation, conduits, pipes, tubing, flow channels, valving, instrumentation, monitoring means, flow regulators, flow controllers, pumps, blowers, ejectors, eductors, aspirators, or the like, as appropriate to the specific end use application of the fluid storage and dispensing assembly of the present invention. The fluid storage and dispensing vessel may be of any suitable size and shape, e.g., a generally cylindrical vessel having an interior volume on the order of from about 0.10 liter to about 100 liters, more preferably in the range of from about 1 liter to about 50 liters.
The interior pressure in the sorbent-containing vessel of the adsorption-desorption apparatus of the invention is below about 1200 Torr. Preferably, the pressure is below 800 Torr, and most preferably below 700 Torr. By providing sub-atmospheric pressure of the sorbed fluid in the storage and dispensing vessel, the risk of leaks and bulk dispersion of the sorbate fluid to the ambient environment is obviated, in contrast to the prior art practice where high pressure containment of the fluid entails a constant and significant risk, and corresponding safety and handling issue.
Another aspect of the present invention relates to a fluid storage and dispensing system comprising a vessel constructed and arranged for holding a physical carbon adsorbent medium having fluid adsorbed thereon, wherein said vessel includes a port having dispensing means associated therewith for controllably dispensing fluid desorbed from the physical adsorbent medium in a dispensing mode of operation of said system, wherein said physical adsorbent medium comprises a low Heel carbon sorbent as described hereinabove. Preferably, such low Heel carbon sorbent is also characterized by a high Sorbate Working Capacity.
The present invention in another aspect relates to a process for supplying a fluid reagent on demand to a fluid-utilizing facility, comprising:
providing a storage and dispensing vessel containing a low Heel solid-phase carbon sorbent medium having a physically sorptive affinity for said fluid reagent;
physically sorptively adsorbing the fluid reagent on the low Heel carbon sorbent medium at an interior gas pressure to yield a sorbate fluid-retaining carbon sorbent medium;
desorbing the fluid reagent from the sorbate fluid-retaining low Heel carbon sorbent medium; and
dispensing the desorbed fluid reagent from said fluid storage vessel.
The low Heel carbon sorbent medium preferably has a high Sorbent Working Capacity.
The low Heel, high Sorbent Working Capacity carbon sorbent material employed in the practice of the invention desirably has the characteristic of readily sorbing the sorbate fluid in the first instance, at suitably high rate, and correspondingly releasing the previously sorbed fluid in a rapid manner in response to (1) a pressure differential between the interior volume of the storage and dispensing vessel and an exterior locus at lower pressure, (2) heating of the carbon sorbent material, and/or (3) flow of a carrier fluid in contact with the carbon sorbent material having sorbed fluid thereon, when the adsorption-desorption apparatus of the present invention is in a fluid dispensing mode of operation.
The carbon sorbent material employed by the present invention demonstrates low Heels and high Sorbent Working Capacity for various sorbate fluids, including but not limited to, arsine (AsH3), boron trifluoride (BF3), germanium tetrafluoride (GeF4), arsenic pentafluoride (AsF5), and trimethyl silane (3MS).
Conventional carbon sorbents, due to their structural limitations, have very high Heels and low Sorbent Working Capacity for these sorbate fluids, which results in undesirable waste and unsatisfactorily low efficiency in transporting and delivering such fluids.
Comparatively, the carbon sorbent material employed by the present invention shows significant advantages over conventional carbon materials in lowering irremovable Heels and concurrently enhancing overall Sorbent Working Capacity, thereby markedly reducing the associated sorption waste rates and increasing the industrial efficiency of the fluid storage and delivery system.
Although the adsorption-desorption apparatus of the present invention is described hereinafter primarily with reference to dispensing fluid from the vessel by pressure differential desorption under a constant temperature, such as room temperature (e.g., xcx9c25xc2x0 C.), it will be appreciated that it may also effect dispensing of fluid by thermally desorbing the fluid from the carbon sorbent material on which it previously has been sorbed. Alternatively, the desorption of the sorbate fluid from the carbon sorbent medium on which it is loaded may be usefully carried out with a combination of pressure differential and thermally-mediated release of the sorbate fluid from the sorbent medium.
The choice of the specific modality of desorption, e.g., pressure differential, thermal, and/or flow-through of carrier fluid, and the appertaining process conditions therefor may readily be selected and determined by the skilled artisan without undue experimentation, based on the nature of the sorbent material, the specific sorbate fluid, and the particular end use application in which the desorbed fluid is to be employed.
Heating means may be operatively arranged in relation to the storage and dispensing vessel for selective heating of the carbon sorbent material, to effect thermally-enhanced desorption of the sorbate gas from the carbon sorbent material. The heating means may include electrical resistance heating elements, extended heat transfer surface members, radiative heating members, or other thermal actuatable heating means disposed in the sorbent bed in the storage and dispensing vessel, or otherwise arranged for transfer or in situ generation of heat to the sorbent material, to effect elevation of the temperature of the sorbent, and desorption of the sorbate fluid.
Additional methods of modifying the carbon sorbent material may be variously employed in the broad practice of the invention to lower the Heel and to increase the Sorbent Working Capacity of said carbon sorbent material, including applying a sorption-enhancing material on the surface (including the interior pore surfaces) of the sorbent material. For example, an adsorption-enhancing liquid, solid, or semi-solid material may be applied to the carbon sorbent material, to further improving its surface property. More specifically, the carbon sorbent material may be fluorinated for more efficient absorption-desorption delivery of arsenic pentafluoride (AsF5) gas, which will lower the Heel by more than 17% and increase the Sorbent Working Capacity by more than 35%.
Other aspects, features and embodiments of the invention will be more fully apparent from the ensuing disclosure and appended claims.